Method of utilizing stainless steel scrap



Patented Oct. 19, 1937 UNITED STATES PATENT OFFKIE 2,096,317 METHOD orUTILIZING s'rammss STEEL sonar Vere B. Browne, Brackenrldge, Pa.,assignor to Allegheny Steel Company, Brackenridge, Pa., a corporation ofPennsylvania No Drawing. Application July 23, 1932,

Serial No. 624,348

5 In the production of chromium iron alloys and chromium nickel alloysof the stainless type the utilization of the scrap resulting from theconversion of ingots of these alloys to various fabricated articles is aserious problem both economically and industrially and is a problemwhich involves many factors.

Most of the chromium alloys of the higher types are madein an electricarc furnace and since chromium has a great afilnity for carbon 1 it isrelatively diflicult to make these alloys with an extremely low carboncontent. On the other hand, the characteristics of these alloys make itnecessary to produce them with a very low carbon content whichconsequently necessitates the 20 use of very expensive low carbonalloying material.

- In the conversion of such alloy ingots into various fabricatedarticles there is from about 40 to 50% of scrap produced and in view ofthe 25 above noted considerations particularly, the remelting of thisscrap cannot be accomplished in the ordinary manner without resulting inthe absorption of carbon by the molten scrap which,

as a result, renders the-product useless for most' 30 purposes. Forexample, there is a large demand for chromium nickel alloy steelcontaining about 18% chromium and 8% nickel and with a carbon content ofless than .10%. In the production of this alloy under the ordinary shopmelting 35 methods it is impossible to utilize scrap of this compositionbecause in melting it down it absorbs a. sufiicient amountof carbon toincrease the content above thelimit of .10% and as a result most of thetonnage of this composition is made 40 by using high priced ierro-chromeand nickel to obtain the required percentage; of these elements. Theresult of these conditions is that there exist relatively largeaccumulations of this scrap which cannot be successfully utilized 4except for the production of alloys for which the demand is ratherlimited.

One of the objects of the present invention, therefore, is theutilization of scrap of the above nature in the preparation of lowcarbon alloy 50 steels.

'Another object resides in a method of making low carbon alloy steels inwhich up to about70% or more scrap in a given furnace charge'can beused. r p 65 A still further object is to make low carbon 13 Claims.(01. 75-127) alloy steels by first producing a melt of steel scrap andadjusting it to extremely lowcarbon content and then combining with thesame a large proportion of stainless scrap and only a relatively smallamount of alloying elements to 5 bring the final composition to thatdesired, while still securing alow carbon alloy.

Other and further objects and advantages 'will either be understood bythose skilled in this art or will be pointed out hereinafter.

I have discovered that I can utilize stainless steel scrap inappreciable amounts up to 70% or more in the making of low carbon alloyswhich thus enables me to produce higher grade alloys at a greatlyreduced cost and at the same time 15 enables me to utilize materialwhich had formerly been of little value due to its very limited uses.

In carrying outthe process of the present invention I first melt down apredetermined per- 2 centage of steel scrap and refine the same under anoxidizing slag until I have reduced the carbon content to approximately.03%. when the carbon content has been reduced to about this figure Iremove the oxide slag from the molten charge and deoxidize and degasifythe molten metal in accordance with the process outlined in my Patent1,658,879. At the completion of this process the low carbon iron iscovered and protected by a thin voluminous calcium aluminate slag whichpretects-the iron from carbon absorption and also serves to protect thechrome nickel scrap which is subsequently added. I 'now addincrementally to the furnace, which may bean electric arc furnace,chrome-nickel scrap having a carbon content which will not be suificientto increase the total carbon content of the final bath above therequired specification.

I make each incremental addition in such a manner that it floats partlysubmerged in the slag, 40 thus burning off any carbonaceous matter withwhich the scrap might be contaminated before each incremental additionis completely submerged inthe protective slag. During this operation thevolume and viscosity of the slag is maintained by suitable additions offluxing reagents, such as alumina, fluor spar, etc. As soon as thepredetermined percentage of scrap has been so melted I add in the samemanner the necessary amount of chromium and nickel to compensate'for theoriginal iron content which was melted at the beginning of the process,In this way I produce and accomplish the above, noted objects andadvantages.

' As an example of the foregoing, 7,000 pounds of steel scrap was melteddown and refined in the manner described until its carbon content waslowered to about .03%. Tothis there was then added in incrementaladditions 10,000 pounds of chrome-nickel alloy scrap containing a carboncontent of approximately 10%. After this was melted, 3,050 pounds offerro-chrome containing .10% carbon was added and also 960 pounds ofnickel. From the above charge there was produced a total weight ofingots of 19,350.

myself thereto other than as contained in the sub-joined claims.

For example, I do not confine myself to melting down the steel scrap inan electric arc furnace asit would be understood by those skilled in theart that I may obtain my initial charge of low carbon iron bytransferring hot metal of the correct composition either from a Bessemerconverter or from an open hearth furnace and thereafter I may thenproceed with the remainder of the steps of the process as explained'herein above.

While I prefer to use the calcium aluminate slag and reduce the ironwith aluminum I may use any suitable slag-forming materials such as limeand fluor spar or lime and sand and I may also use any suitable reducingagent such as silicon or carbon to deoxidize the metal and form areception slag for the, scrap additions.

Similarly I do not confine myself to the limitation of .10% carbon. Itwill be equally well understood by those skilled in the art that theprocess could be applied with advantage to the production of alloys inwhich a more liberal carbon specification is permissible. The processis, however, particularly advantageous and desirable in the productionof alloys specifying an extremely low carbon content, but the process isalso equally applicable to the production of other alloys includingstraight. chrome, chrome tungsten,

chrome molybdenum and any other combination of alloying elements whereit is desirable to utilize the scrap and maintain close limits ofcomposition, especially close limits of carbon content.

What I claim as new and desire to secure by Letters Patent is:

1. In a method of the kind described, melting down a predeterminedpercentage of steel scrap, refining the same under an oxidizing slaguntil the carbon content thereof is reduced to about 0.03%, removing theslag, deoxidizing and degasifying the molten metal, adding a calciumaluminate slag, incrementally adding chrome-nickel steel scrap inpredetermined amount, and bringing the alloying elements of the whole upto the desired content.

2. In a method of the kind described, melting down a predeterminedpercentage of steel scrap, refining the same until its carbon content isabout 0.03%, deoxidizing and degasifying the molten metal, covering themolten metal with suitable slag forming materials, incrementally addinga predetermined amount of chrome-nick- 2,096,81'? & I el alloy scrap,and'finally adjusting the alloy scrap, and finally adjusting the alloycontent of the whole by appropriate additions of alloying elements, saidslag forming materials being calcium aluminate.

4. In a method of the kind. described, melting down a predeterminedpercentage of steel scrap, refining the same until its carbon content isabout 0.03%, deoxidizing and degasifying the molten metal, covering themolten metal with suitable slag forming materials, incrementally addinga predetermined amount of chrome-nickel alloy scrap, and finallyadjusting the alloy content of the whole by appropriate additions. ofalloying elements, said slag forming materialsbeing lime and fluor spar.

5. In a method of the kind described, melting down a predeterminedpercentage of steel scrap, refining the same until its carbon content isabout 0.03%, deoxidizing and degasifying the molten metal, covering themolten metal with suitable slag forming materials, incrementally addinga predetermined amount of bhrome-nickel' alloy scrap, and finallyadjusting the alloy content of the whole by appropriate additions ofalloying elements, said slag forming materials being lime and sand. I 6.In a method of the kind described, 'formin a bath of molten steel,refining the'same until the carbon content is lowered to approximately0.03%

removing the slag formed by the foregoing, so .treating the low carbonmolten iron thus produced as to deoxidize and degasify the same and toform a calcium aluminate reception slag thereon, incrementally chargingportions of chrome nickel scrap onto such-reception slag, while suitablymaintaining the volume and viscosity of the slag, and adjusting thecomposition of the bath by suitable additions containing chromium andnickel.

: such chrome nickel steel scrap.

' elements in suitable proportions and amounts.

9. In a method of utilizing chrome nickel steel scrap to make highquality chrome nickel steel, reducing carbon steel scrap to moltencondition, refining the same to lower the carbon content and to minimizeoxides and gaseous constituents, cov-.

ering the refinedmolten steel with a suitable slag,

adding chrome nickel steel scrap and adjusting the alloy content of themolten steel by appropriate additions of alloying elements. I

10. A method according to claim 9 wherein the slag on the refined moltensteel functions as a reception slag and the chrome nickel steel scrap isincrementally charged onto such reception slag.

11. A method of making alloy steel containing about 18% chromium, about8% nickel and about .10% carbon, with the remainder substantially alliron, comprising forming a molten bath from .carbon-steel scrapcontaining no appreciable I amounts of chromium, reducing its carboncontent to about .03%, reducing .oxide and gas contents to a low value,forming a slag covering over said bath, adding incrementallychrome-nickel alloy steel scrap of approximately the final analysisdesired, and then adjusting the composition of the bath by appropriateadditions of low-carbon ferro-chrome and nickel.

12. A method of making alloy steel of the 18% chromium, 8% nickel, lowcarbon type comprising producing a molten mass of steel with a carboncontent in the neighborhood of .03% and substantially free fromchromium, minimizing oxide and gaseous inclusions, forming a coveringslag onthe molten mass, incrementally charging on the slagchromium-nickel alloy steel scrap of approximately the analysisultimately desired and then making appropriate additions of low-carbonferro-chrome and nickel.

13. A method of the kind described comprising melting down apredetermined amount of carbon steel scrap, refining the same until thecarbon content is reduced to a figure in the neighborhood of .03%,covering this low-carbon bath with a protective slag, partiallysubmerging incremental additions of stainless steel scrap ofapproximately the analysis ultimately desired in said protective slaguntil a total predetermined amount of such scrap has been incorporatedin the bath and then adding alloying ingredients in such kind and amountas will adjust the composition of the bath V

